2009 年 74 巻 4 号 p. 334-343
A gas production system from methane hydrate layers by hot water injection using dual-horizontal wells has been proposed. Experiments with physical and numerical reservoir models have been carried out in order to simulate gas production characteristics with the system. In the experiments, the reservoir models consisting with ice of NaHCO3 aqueous solution formed in glass-bees porous medium were used to express the dissociation heat of methane hydrate by melting one of ice. Gas production at dissociation front of methane hydrate was simulated by a gas generation with the chemical reaction of NaHCO3 included in the ice and HCl mixed in hot water injected at ice melting front.
In the system, a dissociated region including dual horizontal wells filled with hot water, named as hot water chamber, was generated to produce gas continuously. The gas production rate has the maximum peak just after breakthrough of injected water between two horizontal wells, then it declined and gas was produced by almost constant rate.
We have successfully developed the numerical model, and matched the history of physical gas production. Moreover, numerical simulations of gas production by the hot water injection into a field of methane hydrate sediment using dual horizontal wells 500 m in length were carried out for a methane hydrate reservoir of 15 m in layer thickness, 60% of hydrate saturation, 100 md and 25 md in horizontal and vertical absolute permeabilities, respectively. The cumulative gas production is simulated as 1.5 to 1.9×106 m3 std for initial five years, and the total thermal energy injected is 2.3 to 3.5 times of net dissociation energy of methane hydrate. Furthermore, a new gas prodution scheme, which uses four pairs of dual horizontal drilled wells into a methane hydrate sediment with area of 1 km×1 km, has been presented and evaluated with the numerical simulation as the cumulative gas production for 15 years is 1.3×108 m3 std.